Transport-based qubit-array loading

ABSTRACT

When a molecule is lost from a site of a qubit array, the site can be identified as a “target” site. A target site can be reloaded by transporting a molecule from a reservoir at least two millimeters to the target site. Alternatively, in response to the identifying, a molecule that has been transferred from the reservoir to a qubit-array region including the qubit array can be transferred to the target site. Quantum-logic language (QLL) programs can continue qubit operations on the array during transfers from the reservoir to the qubit region. Such operations can also continue during transfer from within the qubit region to a target site; in some cases, these latter operations are limited to sections of the qubit array not including a target site.

BACKGROUND

In part because they operate on qubits that can assume a multitude ofcomplex values as opposed to classical bits, which can only assume apair of values (0 and 1), quantum computers can perform some tasksexponentially faster than their classical counterparts. Ion-based andneutral-atom-based quantum computers have advantages oversuperconductor-based quantum computers in terms of cooling requirementsand manufacturing tolerances (as like-species ions and like-speciesneutral atoms are naturally identical). Neutral atoms have an advantageover ions in that they can be packed closely together withoutinteracting and, yet, be selectively made to interact by exciting themto Rydberg states.

Herein, “molecule” refers to the smallest particle of a substance thatretains all the properties of the substance and is composed of one ormore atoms; this definition, which is set forth in the Merriam WebsterDictionary, encompasses monatomic (single-atom) molecules as well aspolyatomic molecules. Thus, gas-phase alkali (e.g., potassium, rubidium,and cesium) atoms qualify as molecules under this definition. Not usedherein is an alternative and more restrictive definition set forth inthe IUPAC Gold Book: “An electrically neutral entity consisting of morethan one atom”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high-level schematic diagram of a qubit-array system.

FIG. 2 is a more detailed schematic diagram of the qubit-array system ofFIG. 1.

FIG. 3A is a perspective gray-scale representation of a qubit-site arrayof the qubit-array system of FIG. 1 along with optical transportmechanisms used to load molecules into the qubit site array. FIG. 3B isa schematic side-elevational view of a qubit-site array of FIG. 1showing alternative intra-region transport paths from a loading zone toa target site.

FIG. 4 is a flow chart of a transport-based qubit array loading processimplemented in the system of FIG. 1 and in other systems.

FIG. 5 is a gray-scale representation qubit array in which rows are leftvacant so that they can serve as transfer lanes.

FIG. 6 is a gray-scale representation of a qubit array in which all rowsare occupied and in which transfer lanes extend between rows.

FIG. 7 is a flow diagram of a bucket-brigade loading procedure for thequbit array.

FIG. 8A is a gray-scale photograph of a vacuum structure for thequbit-array system of FIG. 1. FIG. 8B is a schematic line drawing of avacuum structure for the qubit-array system of FIG. 1.

FIG. 9A is a gray-scale diagram of the vacuum structure of FIG. 8. FIG.9B is a schematic diagram of the vacuum structure of FIG. 8.

DETAILED DESCRIPTION

The present invention provides for continuous or otherwise minimallyinterruptive use of a molecule-based qubit array while a vacant arraysite is reloaded by transporting one or more molecules from a remotereservoir trap to target sites within the array. Target sites forloading can be identified and then loaded either: 1) directly from thereservoir; or 2) indirectly from the reservoir via a loading zone withina qubit-array region including the qubit array, the molecules to beloaded having been transported from the reservoir into the qubit arrayregion. Typically, the sites identified include at least one site thathas lost a molecule that was serving as a qubit carrier. The reservoircan be spaced at least two millimeters (2 mm) from the qubit-arrayregion so as to avoid undesired interactions that might affect runtimeperformance of the qubit array. The qubit array can be used as aregister in a quantum computer or a quantum simulator; alternatively,the qubit array can be used as an active component of a sensor, anatomic clock, a magnetometer, an electric sensor, a gyroscope, an atomicinterferometer, a positioning or direction-finding device, a signalprocessing device, or other device.

As shown in FIG. 1, a qubit array system 100 includes a qubit-array trap102, a reservoir trap 104, a site identifier 106, and a transport module108. Qubit-array trap 102 provides for a two-dimensional array ofoptical dipole traps; other embodiments provide for one- andthree-dimensional qubit arrays. Qubit-array trap 102, which is disposedin a qubit-array region 110, defines a qubit-site array 112 of qubitsites 114 for storing a qubit array 116 of qubit molecules 118, e.g.,cesium 133 (¹³³Cs) atoms. Reservoir trap 104, which can be an opticaltrap or a magneto-optical trap, can contain a reservoir 120 of molecules122, which may also be ¹³³Cs atoms. Reservoir 120 is disposed within areservoir region 121, which is spaced from qubit-array region 110 by atleast 2 mm to limit disturbance by reservoir molecules 122 of quantumstates of array molecules 118. In an alternative embodiment, thereservoir is spaced less than 2 mm from the qubit-array region.

In other scenarios, other molecules are used, e.g., other alkali andalkaline earth elements: lithium, sodium, potassium, rubidium, cesium,francium, beryllium, magnesium, calcium, strontium, barium, or radium.While the illustrated embodiment provides for use of neutral alkali andalkaline-earth qubits, other embodiments can use other neutral monatomicmolecules, neutral polyatomic molecules, and charged monatomic andpolyatomic molecules (i.e., ions).

Site identifier 106 detects target subsets of one or more sites intowhich molecules are to be loaded; the sites of the target subset caninclude one or more sites from which a molecule of the array has beenlost; in addition, the target subset can include sites that will bevacated as part of the transfer process, e.g., where a bucket-brigadeloading procedure is used. The detection process can be non-destructive,e.g., non-invasive, to avoid unintended alteration of the states ofarray molecules. For example, the target set can contain a single targetsite 124 that site identifier 106 has determined is vacant whileexcluding the rest of the sites in array 112. As long as it excludes atleast one array site, the target subset qualifies as a “proper” subset.

Once a target subset has been identified, transport module 108 cantransport, along a path 128, at least one molecule 130 from reservoirtrap 104 to a respective target site, e.g., site 124, of the targetsubset. Depending on the embodiment, transport of molecules fromreservoir trap 104 to a target site can be direct or can take place insteps and involve one or more intermediate zones. While at least a finalstep of the transport of a molecule into an empty site can involveactive manipulation of the molecule, preceding parts of the transportcan be passive. Passive transport can be mediated by gravity (e.g.,dropping a molecule from reservoir trap to the qubit-array region in agravitational field). Active transport can be mediated by one or more ofmagnetic fields, magnetic field gradients, light pressure, and movingoptical tweezers. Embodiments of transport module 108 that utilizelaser-based transport can include one or more acousto-optical deflectorsand/or one or more spatial light modulators operating holographically oras optical switches.

This transport-based loading allows for continuous operation of qubitarray 116. For example, manipulations (e.g., gate operations, readout)can continue in other parts of array 116 while reloading empty targetsite 124. In one scenario, the occurrence of vacant site 124 due to lossof a molecule is detected by site identifier 106 through non-invasiveoptical readout, and transport module 108 reloads the vacant target site124 with a molecule 130 in response to this loss detection.

As shown in FIG. 2, qubit-array system 100 can include a quantum-gateengine 202 so that system 100 can serve as a gate-model quantum computerand qubit array 116 can serve as a register for the quantum computer.Quantum-gate engine 202 can receive operational instructions from atranspiler 204 that translates generic quantum gates to aquantum-logic-language QLL program 205 of system-specific gateoperations. This transpiler 204 may be configured to take into accountthe current fill status of array 112 and/or ongoing reloading activity.

Transport module 108 includes an inter-region transport module 214having an optical-conveyor-belt generator, and a multi-mode intra-regiontransport module 216, having optical tweezers, a crossed acousto-opticdeflector (AOD), a multi-channel AOD, and a spatial light modulatorgenerators. Inter-region transport module 214 can generate an opticalconveyor belt 218 in the form of a moving standing wave of light.Optical conveyor belt 218 is used to transport, continuously,periodically, or intermittently, molecules from reservoir trap 104 intoqubit-array-region 110, e.g., to a loading zone 220 within qubit-arrayregion 110. Intra-region transport module 216 can generate opticaltweezers 222 (or, depending on mode, crossed AODs, multi-channel AODs,spatial light modulators, electro-optic modulators or liquid crystalmodulators) to move one or more molecules from optical conveyor belt 218(e.g., from loading zone 220) to one or more respective target sites126. In other words, path 128 of FIG. 1 has been divided into twosegments, one associated with conveyor belt 218 and the other associatedwith optical tweezers 222. Optical conveyor belt 218 and tweezers 222are shown in perspective view in FIG. 3A, where loading zone 200 takesthe form of a secondary register.

The intra-region transport can take a variety of paths from loading zone220 to a target site. For example, as shown in FIG. 3B, an “in-line”intra-region transport path 302 extends within the flat volume ofqubit-site array 112, while an “elevated” intra-region transport path304 runs parallel to a plane of the qubit-site array until aligned withthe target site, e.g., target site 124, at which point the transportedmolecule can be transferred orthogonally (e.g., down) to target site124.

To minimize disturbance of qubits, e.g., so that they are notunintentionally driven out of superposition, the loading zone andoptical conveyor belt can be spaced at least 2 mm from the qubit array.Alternatively, one or more of magnetic fields, magnetic field gradients,light pressure, and moving optical tweezers can be used to implement aflow of molecules from the reservoir to the qubit-array region. Thereservoir and the reservoir region can be spaced more than 2 mm, e.g.,10-100 mm, from the qubit-site array and the molecules containedtherein. In other embodiments, this spacing can be less than or equal to2 mm.

A qubit-array loading process 400, flow charted in FIG. 4, includes, at401, transporting cold molecules from a reservoir into a qubit arrayregion containing a qubit-site array. Depending on the mode, this actioncan include transporting over a distance of 10-100 mm or at least over 2mm. Also, this transporting can occur during runtime, that is, while atleast one qubit contained in the array is storing a value computed by aquantum-logic language (QLL) program that the program is configured toread but has not yet read. In some scenarios, during intra-regiontransport of one or more molecules to array sites, circuits and otherqubit operations can continue in array sections that are too distantfrom target sites and reloading paths to be affected by the transport.

At 402, a non-null proper target subset of a set of qubit sites in thequbit-site array is identified. In some embodiments, the identificationis obtained using non-invasive imaging that does not disturb qubitvalues needed for continued runtime operation. “Non-null” means thatthat it includes at least one site, and “proper” means that it excludesat least one site. In many scenarios, the target subset includes one ormore sites from which molecules serving as qubit carriers have beenlost. In some of these, the target set contains only sites from whichmolecules have been lost. In others of these, the target subset caninclude sites from which molecules had not been lost but will have beenvacated in the transfer process, for example, as in a bucket brigadetransfer to be described further below with reference to FIG. 7.

At 403, in response to the identification, at least one molecule istransferred to a target site. In some embodiments, this transfer can bedirectly from the reservoir to the target site. In other embodiments,the transfer can be a transfer from within the qubit-array region to thetarget site. For example, the transfer at 403 can be the second orotherwise last segment of a multi-segment transfer beginning with atransport at 401. Action 403 can include parallel concurrent transfersto plural target sites, e.g., using plural optical tweezers.

The delivery of a molecule into a target site can be directed so thatthe impact on neighboring molecules within a qubit array is negligible.For example, delivery may be implemented along a direction orthogonal toa one or two-dimensional array. Alternatively, or in addition, thedelivery may be accomplished by or facilitated by temporary modificationof the dimensionality, spacing, or other geometric parameters of thearray. For example, the spacing can be increased during transfer toallow more room between rows (or columns) for transfer lanes. Thedelivery may also be accomplished by or facilitated by permanent orintermittent substructures within the array, for instance empty regionsor lanes. The delivery may be enhanced by time-sequenced methodologies.For example, in embodiments where an array trap is an array of dipoletraps and where a transport module utilizes optical tweezers to placeneutral atom in a target site, the delivery can be aided by reducing,removing, or changing frequency of the trapping laser beams during thetransport process or when the tweezer beam has a particular locationwith respect to the array trap.

FIG. 5 illustrates a “structured” loading geometry for system 100(FIG. 1) that reserves some rows of trap sites for reloading transportpurposes. In this reloading geometry, trap sites of qubit-array trap 102are arranged in a plurality of rows, including rows 510 and rows 520.Rows 510 are dedicated to quantum-state carrier-molecules array 112(FIG. 1), whereas rows 520 are left unoccupied to instead be used aslanes for transporting molecules to target sites in rows 510, such asempty site 502. In the example depicted in FIG. 5, each occupied row 510has an adjacent row 520 for transport of a molecule to any target sitesthat occur in row 510. The combined set of rows 510 and 520 may besubstantially equidistant or irregularly spaced.

The loading geometry of FIG. 5 is “structured” in that the arrayincludes features designed to achieve a purpose, in this case, transferlanes that allow molecules to be transferred to a site withoutdisturbing molecules in occupied sites. In the embodiment of FIG. 5, thequbit-site array is regular (and, so, not structured) in that thespacing between adjacent sites is constant across the array. However,the qubit array itself is structured by virtue of not filling rows 520with molecules in a transport-based initial loading scheme. In analternative embodiment, the qubit-site array is structured in that thespacing of qubit sites is not constant across the array so as to leavetransport lanes which minimize disturbance of occupied sites. Thestructuring can be persistent or temporary. For example, a qubit-sitearray and its contents can be temporarily structured to create atransport path in response to a vacancy detection. In one scenario, thespacing of rows including and below (given the orientation in FIG. 5) atarget site can be temporarily compressed to create a transport lanejust above and adjacent to the target site.

FIG. 6 illustrates another loading geometry for system 100 (FIG. 1) thatutilizes transport between rows of trap sites of qubit-array trap 102(FIG. 1). In the loading geometry of FIG. 6, trap sites of the arraytrap are arranged in a plurality of rows 610. When a target site, suchas target site 602 is identified in one of the rows, a molecule istransported to the target site along a path that is between adjacentrows 510. The spacing between rows 610 may be increased dynamicallyduring reloading to accommodate the transport path between rows. Each ofloading geometries of FIGS. 5 and 6 can be realized with one or moreoptical tweezers for moving molecules to target sites. In alternativereloading geometries for two-dimensional arrays, molecules aretransported to target trap sites along paths that are outside the planarvolume of the two-dimensional array.

In FIG. 7, a bucket-brigade transport process 700 is diagrammed for a5×3 site section from the upper left corner (as shown in FIG. 2) ofqubit-site array 112. As shown at 701, site 124 is vacant, while theother sites are occupied. At 702, sites 124, 731 and 732 have beenidentified a target sites. Site 124 has been so identified as it isvacant, presumably due to loss of its molecule. Sites 731 and 732 aredesignated as target sites because they will be vacated temporarilyduring molecule transport.

At 702, molecule 742 has been moved from site 732 to site 124, fillingthe site that lost its molecule, but vacating a neighboring site. At703, molecule 741, which had resided in array site 731, has beentransferred to just-vacated target site 732. At 703, molecule 130 hasbeen transported from loading zone 220 (FIG. 2) to just-vacated targetsite 731 to complete the bucket-brigade transport procedure. Note, thatwhile FIG. 7 shows sequential transfers, in practice, the transfers ofmolecules 742, 741, and 130 can be performed concurrently using threetweezers in parallel. Concurrent transport with plural tweezers can alsobe used to fill plural sites that have been detected to have lostmolecules as part of the identification process. While, for example, abucket-brigade transfer can be implemented using a single opticaltweezer, such a transfer can be implemented faster using plural tweezersin a parallel or pipelined fashion.

To minimize runtime interruptions, some embodiments transport moleculesduring runtime from the reservoir trap to the qubit-array regioncontinuously, periodically or intermittently. In that case, a moleculecan be plucked from the loading zone immediately after a target site isidentified without waiting for a molecule to be transferred from thereservoir trap. In other embodiments, molecules are not transported fromthe reservoir during runtime.

In some embodiments, a transport module provides for transporting amolecule from within a qubit-array region to a target site duringruntime. In some of those embodiments, runtime operation is limited tosections of the qubit array not including target sites. For example, if,as in FIGS. 1, 2, and 7, all target sites are within the upper leftquadrant of the qubit array, program manipulations can be precluded inthe upper left quadrant, but allowed in the other three (upper right,lower left, and lower right) quadrants.

System 100 can be configured to pre-cool molecules prior to loading intotarget site 124; for example to a cold temperature, e.g., below 300microKelvin. In this embodiment, system 100 can deliver a molecule inits motional ground state into target site 124. Reservoir trap 104 canbe configured to cool molecules in reservoir 120 and/or cooling can beapplied to a molecule during its transport to target site 124. Coolingapplied during transport can include Doppler cooling, sideband cooling,evaporative cooling, or other cooling methods known in the art. Coolingapplied during transport can serve to cool a molecule to a temperaturebelow that of reservoir molecules 122 and/or to mitigatetransport-induced heating of molecules.

As shown in the photograph of FIG. 8, qubit-array system 100 includes amolecule supply chamber 802, a pre-cooling cell 804, and a vacuumchamber 806, which is shown in schematic form in FIG. 9. Vacuum chamber806 includes reservoir region 121, and qubit-array region 110. Betweenregions 121 and 110 is baffling 812 to keep scattered light fromreservoir region 121 from interfering with the states of qubit molecules118 (FIG. 1). Baffling 812 is made of and is coated with absorbentmaterials for absorbing light, e.g., including frequencies use toestablish reservoir trap 104.

The separation distance between regions 121 and 110 and the action ofbaffling 812 help maintain high fidelity quantum operations. Theresulting isolation entails implementing physical separation betweenreservoir 120 and qubit register region 110, while also suppressingpropagation of stray/scattered light and/or background gas fromreservoir 120 to qubit-array region 110. Herein, “stray light” refers tolight that is reflected off auxiliary surfaces of the system (such asvacuum-chamber walls), whereas scattered light refers to light that isscattered by molecules (such as molecules 122 in reservoir 120). Inother embodiments, there can be zero or more than one baffle betweenregions 121 and 110.

In addition to or as an alternative to baffling, embodiments provide forsuppressing stray/scattered light using highly transmissive materialsand coatings (e.g., to encourage transmission rather than reflection oflight incident on chamber walls). For example, windows 814 (FIG. 8) usehighly transmissive glass and coatings for this purpose. In addition,elements in addition to baffling 812 can use highly absorptive materialsor coatings.

For scattered light mitigation, system 100 can employ transportgeometries with intermediate transport zones that eliminatelines-of-sight between reservoir trap 120 and qubit register region 116.For example, detour 920 in FIG. 9 converts delivery path 218 into amulti-segment path that avoids a line-of-sight light path betweenreservoir trap 104 and qubit-array region 110.

For gas mitigation, system 100 provides passive and active pumpingbetween qubit register region 116 and a region containing reservoir.Such pumping is, for example, achieved by one or more pumps 924 selectedfrom the groups consisting of ion pumps, sublimation pumps, bulk orsintered getter pumps, and deposited getter coatings. In embodiments, aqubit array region and the reservoir region are separated bydifferential pumping baffling aperture 922, and include additional pumps926 (for example of the types mentioned above) in the qubit arrayregion.

Herein, “non-destructive detection” means detection that does notdisturb any relevant state of a system, which in this case includes themolecules in the qubit array. The relevant state includes the presenceor absence of a molecule at a qubit-array site; therefore, anon-destructive detection would not cause the unintentional loss of amolecule from the qubit array. In the case of runtime operation, therelevant states further include the quantum states of the molecules;thus the non-destructive detection would not cause any molecules to fallout of superposition or otherwise change quantum states of the moleculesin the array. Herein, “cold” molecules have associated temperaturesbelow one milliKelvin. The environment for the reservoir and the qubitarray can be at an ultra-high vacuum (UHV), i.e., below 10⁻⁹ Torr.Herein, “along” implies “not offset from”, while “parallel” implies“offset from” (since “parallel lines never meet”).

Herein, all art labelled “prior art”, if any, is admitted prior art; artnot labelled “prior art”, if any, is not admitted prior art. Theembodiments described herein, variations thereupon, and modificationsthereto are provided for by the present invention, the scope of which isdefined by the following claims.

What is claimed is:
 1. A qubit-array system comprising: a qubit arraytrap including a qubit-site array of qubit sites and configured to trapcold molecules in respective ones of the qubit sites so as to define aqubit array, the qubit-array trap being located in a qubit-array region;a reservoir trap located outside the qubit-array region and configuredto trap a molecules; a site identifier configured to identify a propertarget subset of a set of qubit sites in the qubit-site array, thetarget subset including one or more target sites; and a transport moduleconfigured to, in response to the identifying: transport molecules atleast two millimeters from the reservoir trap to a target site, ortransport a molecule that has been transported from the reservoir trapinto the qubit-array region to a respective one of the target sites. 2.The qubit array system of claim 1 wherein the reservoir trap is spacedat least 2 mm from the qubit-array region.
 3. The qubit array system ofclaim 1 wherein the reservoir is spaced at least 1 0 mm from the qubitarray region.
 4. The qubit array system of claim 3 wherein the reservoirtrap is spaced at most 100 mm from the qubit-array region.
 5. The qubitarray system of claim 1 wherein a target site is vacant due to the lossof a molecule from that site.
 6. The qubit array system of claim 1wherein the target site has been vacated due to removal of a moleculefrom that site to a neighboring site as part of a bucket-brigadeprocedure to fill another target site from which a molecule was lostprior to the identifying.
 7. The qubit-array system of claim 1 whereinthe transport module is configured to transport molecules from thereservoir trap to the qubit-array region during qubit-array runtime. 8.The qubit-array system of claim 7 wherein the transport module isconfigured to preclude, during qubit-array runtime, transport of amolecule that has been transported from the reservoir trap into thequbit-array region to a target qubit site.
 9. The qubit-array system ofclaim 1 wherein the transport module is configured to provide fortransport of a molecule that has been transported from the reservoirtrap into the qubit region to a target qubit site while a programmanipulates qubit values of molecules in a section of the qubit arraynot including a target site.
 10. The qubit-array system of claim 9wherein the transport module is configured to preclude transport of amolecule that has been transported from the reservoir trap into thequbit region to a target qubit site while a program manipulates qubitvalues of molecules in a section of the qubit array including the targetsite.
 11. The qubit-array system of claim 1 wherein the transport moduleis configured to use multiple tweezers concurrently.
 12. The qubit-arraysystem of claim 11 wherein the transport module is configured to use themultiple tweezers to implement concurrent or pipelined loading ofmolecules into respective target sites.
 13. The qubit-array system ofclaim 1 wherein the transport module is configured to use bucket-brigadeloading of a molecule into target site.
 14. The qubit-array system ofclaim 1 wherein the molecules are monatomic molecules.
 15. Thequbit-array system of claim 14 wherein the monatomic molecules areneutral atoms.
 16. The qubit-array system of claim 15 wherein theneutral atoms are of alkali or alkaline-earth elements.
 17. The qubitarray system of claim 1 wherein the site-identifier provides fornon-destructive imaging of the array so as to avoid disturbing thestates of molecules in non-vacant sites in the array.
 18. The qubitarray system of claim 1 wherein the transport module is configured tocool molecules as they are transported from the reservoir.
 19. The qubitarray system of claim 1 wherein the qubit-array is structured so as todefine a transport path to the target site.
 20. The qubit array systemof claim 19 wherein the qubit-array is structured temporarily bycompressing rows or columns of the array.
 21. The qubit array system ofclaim 1 further comprising transmissive materials configured to reducereflections of light from the reservoir region into the qubit-arrayregion.
 22. The qubit array system of claim 1 further comprisingabsorbent materials to absorb light that otherwise could escape thereservoir region into the qubit-array region.
 23. The qubit array systemof claim 1 further comprising gas mitigation using pumps on either sideof a pressure-differential aperture between the reservoir trap and thequbit-array region.
 24. The qubit array system of claim 1 wherein thetransport module includes an intra-region transport module that usesoptical tweezers, crossed acousto-optic deflectors, multi-channelacousto-optic deflectors, spatial-light modulators, electro-opticmodulators or liquid crystal modulators.
 25. The qubit array system ofclaim 1 wherein the transport of a molecule to a target site ispartially along a plane through all qubit-sites of the qubit-site array.26. The qubit array system of claim 1 wherein the transport of amolecule to a target site is partially parallel to a plane through allqubit sites of the qubit-site array.
 27. The qubit array system of claim26 wherein the transport of the molecule to the target site is partiallyorthogonal to the plane through all qubit sites of the qubit-site array.28. A qubit-array loading process comprising: transporting moleculesfrom a reservoir trap into a qubit-array region, the qubit-array regioncontaining a qubit-site array, the qubit-site array containing a set ofqubit sites, the reservoir trap being located in a reservoir region;identifying a proper target subset of the set of qubit sites, the targetsubset including one or more target qubit sites; and in response to theidentifying, transporting a molecule from the reservoir trap a distanceof at least two millimeters to a respective target site, or a moleculethat has been transported from the reservoir trap into the qubit regionto a respective target site.
 29. The qubit array loading process ofclaim 28 wherein transporting from the reservoir trap to the qubit-arrayregion is over a distance of at least 2 mm.
 30. The qubit array loadingprocess of claim 28 wherein the transporting from the reservoir trap tothe qubit-array region is over a distance of at least 10 mm.
 31. Thequbit array loading process of claim 30 wherein the reservoir trap isspaced at most 100 mm from the qubit-array region.
 32. The qubit arrayloading process of claim 28 wherein a target site is vacant for theduration of the transport from within the qubit-array region to thetarget site.
 33. The qubit array loading process of claim 28 wherein thetarget site has been vacated due to removal of a molecule from that siteto a neighboring site as part of a bucket-brigade procedure to fillanother target site that was vacated due to loss of a molecule from thearray.
 34. The qubit-array loading process of claim 28 whereintransporting molecules from the reservoir trap to the qubit-array regionoccurs during qubit-array runtime.
 35. The qubit-array loading processof claim 34 wherein the transporting precludes, during qubit-arrayruntime, transport to a target site of a molecule that has beentransported from the reservoir trap into the qubit region.
 36. Thequbit-array system of claim 28 wherein the transporting includesmanipulating qubit values of molecules located in sections of the qubitarray not including a target site while a molecule is transported to atarget site.
 37. The qubit-array system of claim 36 wherein thetransporting precludes transport of a molecule that has been transportedfrom the reservoir trap into the qubit region to a target site while aprogram manipulates qubit values of molecules in a section of the qubitarray including the target site.
 38. The qubit-array loading process ofclaim 28 wherein the transporting includes using multiple tweezersconcurrently.
 39. The qubit-array loading process of claim 38 whereinthe transporting uses the multiple tweezers to implement concurrent orpipelined loading of molecules into respective target sites.
 40. Thequbit-array loading process of claim 28 wherein the transportingincludes loading of a molecule into a target site using a bucket-brigadeprocedure.
 41. The qubit-array loading process of claim 28 wherein themolecules are monatomic molecules.
 42. The qubit-array loading processof claim 41 wherein the monatomic molecules are neutral atoms.
 43. Thequbit-array loading process of claim 42 wherein the neutral atoms are ofalkali or alkaline-earth elements.
 44. The qubit array loading processof claim 28 wherein the identifying includes using non-destructiveimaging of the array so as to avoid disturbing the states of moleculesin non-vacant sites in the array.
 45. The qubit array loading process ofclaim 28 wherein the transporting includes cooling molecules as they aretransported from the reservoir.
 46. The qubit array loading process ofclaim 28 wherein the qubit-array is structured so as to define atransport path to the target site.
 47. The qubit array loading processof claim 46 wherein the qubit-array is structured temporarily bycompressing rows or columns of the array.
 48. The qubit array loadingprocess of claim 28 further comprising transmitting light throughtransmissive materials to reduce reflections of light from the reservoirregion into the qubit-array region.
 49. The qubit array loading processof claim 28 further comprising absorbing, by absorbent materials, lightthat otherwise could escape the reservoir region into the qubit-arrayregion.
 50. The qubit array loading process of claim 28 furthercomprising mitigating gas using pumps on either side of apressure-differential aperture between the reservoir trap and thequbit-array region.
 51. The qubit array loading process of claim 28wherein the transporting uses optical tweezers, crossed acousto-opticdeflectors, multi-channel acousto-optic deflectors, spatial-lightmodulators, electro-optic modulators or liquid crystal modulators. 52.The qubit array loading process of claim 28 wherein the transport of amolecule to a target site is partially along a plane through allqubit-sites of the qubit-site array.
 53. The qubit array loading processof claim 28 wherein the transport of a molecule to a target site ispartially parallel to a plane through all qubit sites of the qubit-sitearray.
 54. The qubit array loading process of claim 53 wherein thetransport of the molecule to the target site is partially orthogonal tothe plane through all qubit sites of the qubit-site array.